Sweet Potato and Gruyère Gratin

1. Prepare Baking Dish

Preheat the oven to 400 degrees F (200 degrees C). Grease a 9-by-13-inch baking dish with unsalted butter and sprinkle the bottom evenly with grated Parmesan cheese.

2. Create Cream Mixture

In a medium pot, combine heavy cream, chopped sage, chopped rosemary, minced garlic, grated nutmeg, and a pinch of salt. Simmer for 10 minutes until reduced by about a quarter, stirring occasionally.

3. Combine Eggs and Cream

In a large bowl, lightly beat the eggs. Gradually whisk the reduced cream mixture into the eggs until combined.

4. Layer the Gratin

Arrange a layer of thinly sliced sweet potatoes in the prepared baking dish. Season with salt and freshly ground pepper. Pour a portion of the egg and cream mixture over the sweet potatoes and sprinkle with grated Gruyère cheese. Repeat layering until all ingredients are used, ending with sweet potatoes topped with Gruyère cheese.

5. Bake the Gratin

Cover the dish with foil and bake in the preheated oven for 40 minutes. Remove the foil and continue to bake for another 25 to 30 minutes until the top is golden brown and bubbly. Let the gratin cool slightly before serving.